Phase I involves manufacturing and testing a Rolling Joint Prosthetic Leg (RJ Leg), comprisingly a newly developed Rolling Joint Foot (RJ Foot) and Rolling Joint Knee (RJ Knee). Prosthetic rolling joints will significantly impact the comfort and independence of the transtibial and transfemoral amputees and increase the number of persons, especially elderly, able to wear lower limb prostheses. The specific aims of the project. (1) Manufacture the RJ Knee prototype, which mechanism yields a resistive curve similar to the biological knee joint. (2) Mechanically test stance flexion of the RJ Knee, and shock absorption, rotational stiffness and eversion/inversion of the RJ Foot. (3) Conduct a biomechanical study of 405 transfemoral (AK) amputees wearing a RJ Leg prototype and comparing it to their existing prostheses on: normalizing range of motion in the knee joint; decreased peak pressures between residuum and a socket. This will increase functionality of the leg prosthesis by normalizing the synergetic relationship between the motion in prosthetic ankle and knee during the stance phase of the gait. Long term objectives of the proposed research, are to: develop a functional, reliable and economical prosthetic leg modular system, and a system for synergetic alignment of the components. PROPOSED COMMERCIAL APPLICATION Potential commercial applications is the creation of a product line of Rolling Joint Feet and Knees. The RJ Leg will enhance performance of amputees without increasing cost, thus providing a highly competitive product in the field of prosthetic rehabilitation.